I liked it so far, I have installed mine for 3 months and don't think I can live without it from now on. It simply takes the hard labor out of daily kalk mixing and dosing and adjusting of it.
As with manual kalk dosing, you do have to monitor ph and alk periodically. I have mine feeding off a litemeter which in turns was controlled by a liquid level sensor.
I have never used one, but I see little advantage of them over a big limewater tank, unless space is an issue. I use a 44 gallon limewater trash can that lasts about 2-3 weeks. If you keep excess solid on the bottom, it stays close to saturation (if you actually need saturated limewater; I typically don't).
